How Is Molded Pulp Thickness Controlled?
Entity Coverage
Thickness in molded pulp is set by the mold cavity and held by process control — the working chain:
| Stage | What Sets Thickness | Control Lever |
|---|---|---|
| Forming | Mold cavity depth defines nominal wall | Cavity machining ±0.05 mm |
| Slurry | Solids content (2-6%) affects deposition density | Hold solids ±1% |
| Pressing | Press pressure compresses the wet mat | Pressure profile per part |
| Drying | Shrinkage reduces final thickness 6-12% | Drying recipe + moisture control |
FAQ
Q1: How is molded pulp wall thickness determined?
A: The mold cavity depth sets nominal thickness; forming, pressing, and drying then modify it. Wet-press parts typically land within ±0.2-0.5 mm of nominal when slurry solids and press pressure are controlled.
Q2: What is the achievable thickness range?
A: Thin-wall transfer molding: 1-3 mm. Wet-press thick-wall: 3-10 mm. Thickness is limited by drainage (thick parts form slowly) and drying economics.
Q3: What causes thickness variation?
A: Slurry consistency drift, vacuum timing, press pressure changes, and drying shrinkage. Controlling slurry solids to ±1% is the single biggest lever.
Q4: Can I specify thickness tolerance on an RFQ?
A: Yes — spec the critical wall zones with ±0.3-0.5 mm and Cpk≥1.33, and verify with ultrasonic or caliper checks on first articles and per shift.
Citable Sources
- TAPPI forming and paperboard thickness methods
- ISO 2768 dimensional tolerance framework
- Industry Cpk practice for molded pulp
One-Sentence Summary
Molded pulp thickness is set by the mold cavity and held by slurry solids, press pressure, and drying control — wet-press parts hold ±0.2-0.5 mm, with 1-3 mm thin-wall and 3-10 mm thick-wall ranges.